EAST Park's paddling pool has been closed after several children who visited it were infected with parasites.
Since mid-July, 18 people – mainly children – have been diagnosed with cryptosporidiosis, an illness which causes diarrhoea.
Although the cause of the infection is not yet known, a city council investigation has revealed some of the infected children had visited East Park.
Its paddling pool has now been shut for emergency cleaning and maintenance.
Dr Autilia Newton, consultant in communicable disease control at Public Health England, said: "We are working with environmental health officers from Hull City Council to investigate any possible common sources of infection, but it is not possible to confirm the source of the infections at this time.
"Cryptosporidium is a parasite that causes an infection called cryptosporidiosis.
"The most common symptom is watery diarrhoea, which can range from mild to severe. Other symptoms can include abdominal pain, nausea and fever or general malaise."
Cryptosporidium is found in soil, food, water, or on surfaces that have been contaminated with infected human or animal faeces.
The infection is passed on through animal-to-human or human-to-human contact.
People can also be infected by consuming contaminated water or food, or by swimming in contaminated water.
Infection is frequently associated with foreign travel.
Andrew Taylor, acting director of public health at Hull City Council, said: "To date, we have learnt that a number of those who have been ill have recently visited East Park.
"As a precautionary measure, the council has decided to temporarily close the paddling pool in the park for additional cleaning and maintenance work.
"This is a precautionary measure and it is not possible to confirm the source of the infections at this time."
The illness is not life-threatening and usually persists for about a month.
It particularly affects young children.
Dr Newton said: "Cryptosporidiosis is most common in children aged between one and five years, but it can affect anyone.
"There is no specific treatment for cryptosporidiosis but it is important for anyone who is infected to drink plenty of fluids to avoid dehydration. Most people with a healthy immune system will recover within one month.
"We would advise anyone suffering from cryptosporidiosis to avoid mixing with others outside their home – for example, attending a nursery or childminder – until 48 hours after diarrhoea symptoms have stopped. It is also advisable to particularly avoid swimming until two weeks after the diarrhoea has settled.
"Parents need to make sure they have thoroughly washed their hands after changing nappies or cleaning children's bottoms if they have diarrhoea."
The disease is caused by a waterborne parasite.
It is almost never fatal in the developed world but can be dangerous for people with poor immune systems, particularly Aids sufferers, who may develop much more severe cholera-like symptoms.
There was a rise in the disease last summer, with 267 cases of cryptosporidiosis in a month in four areas, including East Yorkshire, compared with 73 across the same four regions in 2011.
In 2005, the bug entered 70,000 homes through the water supply in North Wales.
Visit www.hpa.org.uk for more information.
